-
Molecular Deuteration on grain surfaces
Project Investigators: Jacqueline Keane, Xander Tielens, Berenger Parise
Summary
n recent years, deuterium fractionation has been instrumental in deciphering the main chemical routes in molecular clouds. This fractionation reflects the small zero-point energy difference (a few hundred Kelvin) between deuterated species and fully hydrogenated species. At low temperatures, this can enhance the abundance of deuterium-bearing species by many orders of magnitude. In fact, recent observations of deuterated water have revealed that it is consistently less fractionated than other species by factors ranging from 10 to 100. Paralleling this, large deuterium fractionation effects are seen, most notably for deuterated forms of formaldehyde, methanol and ammonia versus their fully hydrogenated forms. Motivated by this, we have expanded our Monte Carlo accretion model to include deuterium chemistry in order to explore the role of grain surface chemistry in selectively deuterating ammonia and methanol as opposed to water.
Astrobiology Roadmap Objectives:
Project Progress
A key aspect of the grain surface chemistry’s role in the selective fractionation of methanol over water centers around the H2 or HD on the grain surface. This adsorbed H2/HD can cause an ozone cascade that preferentially channels a significant fraction of atomic H into reactions with ozone (O3) resulting in water. Paralleling this, atomic deuterium is selectively channeled into reactions with co-reactants (predominantly formaldehyde, methanol and ammonia) that have lower activation barriers as a result of the zero-point energy difference between atomic hydrogen and deuterium. An important consequence of this reaction scheme is that the formation of deuterated water (both HDO and D2O) is not favored. Significant progress on this project has been made in comparing our model results with recent observations of deuterated isotopologues of ammonia and water toward the embedded low mass protostars IRAS 16293-2422.
Comparison of observations of ammonia isotopologues detected toward a number of embedded protostars with our model results. The model suggests that the deuteration of ammonia occurs for a deuterium/hydrogen ratio of around 0.1 when the cloud density is around 10^4 cubic centimeters.Our grain surface model can accurately account for the enhanced deuteration of ammonia while also reproducing the low fractionation of water. This good agreement demonstrates that grain surface reactions are instrumental in causing significant fractionation for a selective set of molecules.
![Other Projects](https://webarchive.library.unt.edu/eot2008/20090825102738im_/http://astrobiology.nasa.gov/img/text/hd_other_projects_sa.gif)
- HANDBOOK OF STAR FORMING REGIONS
- A Rare low mass quadruple spectroscopic AND eclipsing binary
- A search for Main Belt Comets in Pan-STARRS 1
- A search for primordial water from deep in the Earth's mantle
- A spectroscopically unique Main Belt asteroid: 10537 (1991 RY16)
- A Supertree Analysis of the Metazoan Phylogeny
- Acquisition and Installation of a new Cameca ims 1280 ion microprobe
- Acquisition and Installation of Witec Confocal Raman microscope scanning system
- Amorphization of Crystalline Water Ice in the Solar System
- Assessing the likelihood of supernova impact of protoplanetary disks
- Carbonate Lithologies on Devon Island, Canada
- Chemistry and biology of ultramafic-hosted alkaline springs
- Chemistry of the NH3/H2O system
- DIVERSITY AND BIOGEOGRAPHY OF THE UNIQUE TROPICAL PHYLUM PLACOZOA
- Dynamical Evolution of Astroid Belt and the Parent Bodies of Iron Meteorites
- Ecology of a Hawaiian lava cave microbial mat
- FMARS Long Duration Mission: a simulation of manned Mars exploration in an analogue environment, Devon Island, Canada
- Formation and Detection of Hot-Earth Objects in Systems with Close-in Jupiters
- Formation and the Prospects of the Detection of Habitable Planets in Extreme Planetary Systems
- Formation of Molecular Hydrogen via Interaction of Ionizing Radiation with Hydrocarbon Ices in the Interstellar Medium
- Formation of Planetesimals in a Dynamically Evolving Nebula
- FU ORIONIS ERUPTIONS
- Ice Ages on Mars
- Ice at the Mars Phoenix Landing Site
- Ice on Main Belt Comets
- Icelandic subglacial lakes
- Mechanisms of Marine Microbial Community Structuring
- Mechanistical Studies on the Non-Equilibrium Chemistry of Unusual Carbon Oxide in Solar System Ices
- Modeling grain surface reaction pathways for large organic molecules
- Molecular Deuteration on grain surfaces
- NEWBORN BINARIES
- Observations and Models of comet 17P/Holmes
- Origin and Activation Mechanism of Main Belt Comets
- Origin of Irregular Satellites
- Recovery of comet 85P/Boethin for the Deep Impact Extended Mission
- Sediment-buried basement deep biosphere
- Serpentinazation and abiogenic methane in the Mariana Forearc
- Sleeping through the Arctic Martian Sol
- Spectropolarimetric studies of stars with hot jupiters
- TES study of intracrater low albedo deposits, Amazonis Planitia, Mars
- The delivery of short-lived radionucleides to the solar system
- The effect of lunar-like satellites on the orbital infrared lightcurves of Earth-analog planets
- The Main Belt distribution of basaltic asteroids
- The Size Distribution of Small KBOs
- THE VYSOS PROJECT
- Ultra-violet processing of ices in the Rosette Nebula
- Unveiling the evolution and interplay of ice and gas in quiescent clouds
- Variable Young Stellar Objects Survey (VYSOS)
- Water on Mars
- X-ray- and UV-bright low-mass stars in the solar neighborhood